1. Field of the Invention
The present invention relates to a probe system for electrically testing an object to be tested, such as a semiconductor wafer.
2. Description of the Related Art
Typically as shown in FIGS. 4A and 4B, a conventional probe system comprises a loader unit 1 for carrying and pre-aligning a wafer W, and a probe unit 2 for receiving the wafer W from the loader unit 1 to electrically test the wafer W. The loader unit 1 is provided with tweezers 3 and a sub-chuck 4. While the wafer W is carried by the tweezers 3, the wafer W is pre-aligned in the sub-chuck 4 on the basis of an orientation flat or notch.
The probe unit 2 is provided with a main chuck 5 and an alignment mechanism 6. A probe card 7 is detachably mounted on a head plate 8 which forms a ceiling of the probe unit 2. The main chuck 5 supporting thereon the wafer W is designed to move in directions X, Y, Z and xcex8 (rotation about a vertical axis). The alignment mechanism 6 is designed to align the wafer W on the main chuck 5 with respect to probe needles 7A of the probe card 7. By causing the wafer W to electrically contact the probe needles 7A, electric characteristics of the wafer W are tested by means of a test head T.
The loader unit 1 is adjacent to the probe unit 2 via a partition wall 9. The partition wall 9 is provided with an opening 9A having a shutter. This shutter is designed to be open when the wafer W is transferred between the loader unit 1 and the probe unit 2 by means of the tweezers 3.
Tests of wafers W by the probe systems include a low temperature test and a high temperature test in addition to a room temperature test. Therefore, the main chuck 5 includes a temperature control mechanism. By using this temperature control mechanism, the temperature of the wafer W can be controlled in the range of from xe2x88x92tens xc2x0 C. to +160xc2x0 C. For example, when a low temperature test at xe2x88x9240xc2x0xc2x0 C. is carried out, the wafer W on the main chuck 5 is cooled to xe2x88x9240xc2x0 C. by the temperature control mechanism. At this time, if no measures are taken, water vapor in air condenses and freezes on the surface of the wafer W. Thus, after dry air is filled in the probe unit 2, the dry air is circulated to prevent dew condensation and/or freezing.
For example, as shown in FIG. 4B, the probe unit 2 is provided with a fan filter unit (FFU) 2A and a circulating duct 2B for circulating dry air supplied to the interior of the probe unit 2, via the circulating duct 2B. Particles produced in the probe unit 2 and mixed in the dry air are removed by the filter of the FFU 2A.
However, in the case of such a method for circulating dry air, if the flow rate of circulating dry air is increased to improve cleanliness in the prove unit 2, it is not possible to expect a low dew point. Conversely, if the flow rate of circulating dry air is decreased to obtain a lower dew point, it is not possible to maintain cleanliness. Moreover, if the probe unit 2 is provided with both of the FFU 2A and the circulating duct 2B, costs are increased. In addition, when the wafer w is returned to the loader unit 1 from the probe unit 2, there is a possibility that water vapor in the loader unit 1 may condense and/or freeze on the cold wafer W.
It is therefore an object of the present invention to eliminate the aforementioned problems and to provide a probe system capable of preventing dew condensation and/or freezing on an object to be tested in a low temperature test while maintaining cleanliness in a probe unit, and capable of reducing production costs.
In order to accomplish the aforementioned and other objects, according to one aspect of the present invention, there is provided a probe system comprising: a probe unit having a case defining a prober chamber for receiving an object to be tested, and a contact probe for testing the object received into the prober chamber; and a loader unit having a case defining a loader chamber partially communicated with the prober chamber, and a carrying mechanism for carrying the object between the prober chamber and the loader chamber, wherein the loader unit further has a main shielding cover for covering the carrying mechanism in the loader chamber, and the probe system further comprises means for supplying dry air via a filter into an interior of the main shielding cover of the loader unit and the prober chamber.
In the above described probe system, the loader unit preferably has an alignment mechanism for aligning the object, the alignment mechanism being covered with the main shielding cover in the loader chamber.
In the above described probe system, the main shielding cover is preferably rotatable together with the carrying mechanism.
In the above described probe system, the case of the loader unit preferably has an opening for communication with the prober chamber, and the loader unit preferably has an auxiliary shielding cover for covering a space between the main shielding cover and the opening to define a carrying passage for the object. In this case, the opening is provided with a door for selectively closing the opening.
The above described probe system preferably further comprises means for supplying clean air into the loader chamber.